Deal earned few songwriting credits in the Pixies and sang lead vocals on even fewer, but Gigantic, from the band's 1988 debut album Surfer Rosa, was among their best moments: jaw-droppingly sexual ("my big, big love") and catchier than a medieval plague. Deal's breathy voice, which provided a sensual contrast to Black Francis's bloodcurdling screams on the rest of the Pixies' catalogue, was here allowed centre stage, and it was a relief – shocking, even.

Pixies were groundbreaking and original at a time when rock music had seemed moribund. They used unconventional chord structures and time signatures, but they never forgot to write a tune. Chief among their innovations was their use of dynamics. Having a hushed verse followed by a sudden, deafening chorus seems obvious post-Nirvana, but the Pixies were the ones who pioneered it. And during those quiet bits it was always Deal's snaking, four-to-the-floor bass-lines always kept the show on the road, allowing Black Francis to pant and yelp his frightening Old Testament lyrics about sex and death before the chorus's ecstatic eruption.

The band didn't go in for stage tricks or dazzling light shows. Black Francis was an unlikely-looking frontman as it was. But onstage, Deal provided reassurance, grinning her way through songs that were often genuinely unnerving.

After the Pixies' first break up in 1993 – Francis notoriously informed the other band members by fax – it came as no surprise when Deal's side project the Breeders made records that were the equal of the Pixies. Last Splash showed how inventive, contrary, funny she could be, not to mention effortlessly cool. People asked, why didn't the Pixies make more of her? After all, her talent had been there to hear on Gigantic.

When the Pixies reconvened in 2004 a new song, Bam Thwok, was released with Deal on vocals once more. Many fans hoped it heralded a new era of Pixies songs with a more central role for Deal, but it was not to be. The Pixies were still a thrilling live prospect, but the sets focused on early classics Come On Pilgrim (an eight-song EP from 1987), Surfer Rosa and 1989's Doolittle. A 2006 documentary, loudQUIETloud: a film about The Pixies, showed the tensions between the group were as alive as ever.

With renewed interest in the Breeders (it's the 20th anniversary of Last Splash) today's announcement of Deal's departure from the Pixies is perhaps expected. You wouldn't bet against the other Pixies continuing to perform and even recording together again. But it won't be the same.